1. Field of the Invention
The present invention relates to a media access controller, and more particularly, to a media access controller, which can adjust operation parameters according to a setting environment of a packet transmission system by re-setting the operational parameters of the media access controller externally.
2. Description of the Related Art
FIG. 1 illustrates a conventional embodiment in which a plurality of packet transmission stations are connected to a shared medium. When a plurality of packet transmission stations use a shared medium, a media access control (MAC) protocol is used to facilitate communication and prevent collisions among the stations.
A CSMA/CD algorithm is widely used as a MAC protocol of IEEE 802.3 in wired local area networks and a CSMA/CA algorithm is widely used as a MAC protocol of IEEE 802.11 in wireless local area networks. In a representative home network standard, i.e., a 10 Mbps home phone-line networking alliance (HomePNA) standard, the CSMA/CD algorithm augmented by a priority control algorithm and a distributed fair priority queuing (DFPQ) collision resolution algorithm is widely used.
FIG. 2 is a block diagram of a conventional packet transmission system. Most packet transmission stations are often called a packet transceiver and correspond to the stations illustrated in FIG. 1. The packet transmission system has frame generation, scrambling, and modulation functions for sending packets, and demodulation, descrambling, and deframing functions for receiving packets.
Also, since the packet transmission system shares a medium as illustrated in FIG. 1, the packet transmission system includes a MAC 21, a collision detector 22, which informs the MAC 21 if a collision occurs, a carrier sensor 23, which generates a carrier sense signal, and a manager 24, which monitors the whole system, sets specific registers to predetermined values, and reads the specific registers.
FIG. 3 illustrates an example of a multiple media access control having a transmission priority. When transmission priorities of stations are not determined, a collision rate is very high, and since there is no solution involving prioritization of data, quality of service (QoS) is very low. In FIG. 3, a highest priority is priority 7 and a lowest priority is priority 0. Since a priority of 6 [Tx_PRI=6] is assigned to a station 1 (STA1), data of the STA1 is transmitted first, data of a station 2 (STA2) having a priority of 5 [TX_PRI=5] is transmitted next, and then data of a station 3 (STA3) having a priority of 3 [TX_PRI=3] is transmitted last.
FIGS. 4a through 4c illustrate timeslots of a HomePNA. A 1 Mbps HomePNA standard version 1.0 was announced in September 1998, a 10 Mbps HomePNA standard version 2.0 was announced in December 1999, a 10 Mbps HomePNA standard version 2.1 was announced in August 2001, and a 100 Mbps HomePNA standard version 3.0 was announced in August 2003.
FIG. 4a is a timeslot of a case where there are no collisions among stations, the timeslot defined in the HomePNA standard versions 2.0/2.1. FIG. 4b is a timeslot after a collision among stations, the timeslot defined in the HomePNA standard version 2.0. FIG. 4c is a timeslot after a collision among stations, the timeslot defined in the HomePNA standard version 2.1. In FIG. 4b, an inter-frame gap (IFG) comes just after a collision frame, but in FIG. 4c, the IFG comes after 92 μs, which includes the collision frame.
A timeslot is a transmission time unit used in a media access controller (MAC) as illustrated in FIGS. 4a through 4c. A sending station sends data at an appropriate timeslot using the timeslot. Also, the timeslot is used for identifying which timeslot an input frame uses. When applied standards are changed as illustrated in FIGS. 4b and 4c, compatibility between a design to which a prior standard is applied and a design to which an updated standard is applied must be considered. Also, since HomePNA standards define the maximum number of stations capable of concurrently connecting to a shared medium as 25 but the number of bits of a back-off counter used for resolving collisions as 4, the maximum number of simultaneously colliding stations is limited to 15.
However, due to increasing popularity of home networks and improvements in physical layer products, the maximum number of stations and bits of a back-off counter will likely increase. Therefore, there is need for a new apparatus capable of ensuring QoS now and in the future and of dealing with standard changes.